Contact magnetic transfer template

ABSTRACT

A contact magnetic transfer (CMT) master template has a flexible plastic film with a planarized top or upper surface containing magnetic islands separated from one another by nonmagnetic regions. The flexible plastic film is secured at its perimeter to a silicon annulus that provides rigid support at the perimeter of the film. The plastic film is preferably polyimide that has recesses filled with the magnetic material that form the pattern of magnetic islands. The upper surfaces of the islands and the upper surfaces of the nonmagnetic regions form a continuous planar surface. The nonmagnetic regions are formed of chemical-mechanical-polishing (CMP) stop layer material that remains after a CMP process has planarized the upper surface of the plastic film.

RELATED APPLICATION

This application is related to concurrently filed application Ser, No.,11/044,288 titled “METHOD FOR MAKING A CONTACT MAGNETIC TRANSFER,/TEMPLATE”, which has issued as U.S. Pat No. 7,160,477 B2.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a master template for contactmagnetic transfer of magnetic patterns and to a method for making thetemplate.

2. Description of the Related Art

Contact magnetic duplication or transfer (CMT), sometimes referred to asmagnetic printing, is a method of instantaneous recording of magneticpatterns onto magnetic media. In a magnetic recording hard disk drive,each disk contains a fixed, pre-recorded servo pattern of magnetizedservo regions or blocks that are used to position the recording head tothe desired data track. In the CMT method for forming the servo patterna “master” disk or template is used that contains regions or islands ofsoft (low-coercivity) magnetic material in a pattern corresponding tothe servo pattern that is to be transferred to the magnetic recordingdisk (the “slave” disk).

The CMT master template is typically a rigid substrate or a rigidsubstrate with a plastic film formed on it. These types of mastertemplates have been described in U.S. Pat. Nos. 6,347,016 B1 and6,433,944 B1; Japanese published application JP2002-342921; and byIshida, T. et al., “Magnetic Printing Technology-Application to HDD”,IEEE Transactions on Magnetics, Vol 39, No. 2, March 2003, pp 628-632.

In U.S. Pat. No. 6,798,590 B2, assigned to the same assignee as thisapplication, a CMT method is described that uses a flexible mastertemplate and a differential gas pressure to press the pattern ofmagnetic islands against the slave disk. The pattern of magnetic islandsis formed on the template by electroplating or evaporation of themagnetic material through a resist pattern, followed by liftoff of theresist. However, this process can result in variations in the surfacesof the magnetic islands and irregularities in the shape of the magneticislands.

What is needed is an improved CMT master template and method for makingit.

SUMMARY OF THE INVENTION

The invention is a CMT master template that has a flexible plastic filmwith a planarized top or upper surface containing magnetic islandsseparated from one another by nonmagnetic regions. The flexible plasticfilm is secured at its perimeter to a silicon annulus that providesrigid support at the perimeter of the film. The plastic film ispreferably polyimide that has recesses filled with the magnetic materialthat form the pattern of magnetic islands. The upper surfaces of theislands and the upper surfaces of the nonmagnetic regions form acontinuous planar surface.

The template is made by first adhering the plastic film to a firstsurface of a silicon wafer, such as by spin-coating liquid polyimidefollowed by curing. A resist pattern is then formed on the polyimidefilm and the polyimide is reactive-ion-etched through the resist to formrecesses. The resist is removed and a chemical-mechanical-polishing(CMP) stop layer is deposited over the non-recessed regions of thepolyimide, and optionally into the bottoms of the recesses. A layer ofmagnetic material is then deposited over the polyimide film to fill therecesses. A CMP process is then performed to remove magnetic materialabove the recesses and above the non-recessed regions and continueduntil the CMP stop layer is reached. The resulting upper surface of thepolyimide film is then a continuous planar film of magnetic islands andregions of CMP stop layer material that function as the nonmagneticregions. The central portion of the silicon beneath the polyimide filmis then removed to leave just the annular silicon portion supporting thepolyimide film at its perimeter. The preferred removal process for thesilicon is to wet etch the silicon wafer from its second surface. Abarrier layer may be deposited on the first surface of the silicon waferprior to the polyimide film. When the central portion of the siliconwafer is removed by wet etching from its second surface the wet etchingis terminated when the barrier layer is reached so that the polyimidefilm is not attacked by the etchant. If the silicon substrate is removedin this manner, then the resulting master template has the barrier layerremaining on its bottom or lower surface.

For a fuller understanding of the nature and advantages of the presentinvention, reference should be made to the following detaileddescription taken together with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B are a plan view and a partial sectional view, respectively,of a hard magnetic recording disk illustrating a pattern of servosectors extending generally radially across an annular data band.

FIG. 2 is an expanded view of one of the servo sectors of FIG. 1Ashowing the magnetized servo regions or blocks.

FIG. 3 is a side sectional view of the CMT apparatus used with the CMTmaster template made according to the method of the present invention.

FIGS. 4A-4K are sectional views showing the steps in a first embodimentof the method for making the CMT master template of the presentinvention.

FIGS. 5B, 5C, 5D, 5G and 5H are sectional views showing the steps in asecond embodiment of the method for making the CMT master template forcomparison with corresponding FIGS. 4B, 4C, 4D, 4G and 4H.

DETAILED DESCRIPTION OF THE INVENTION

A typical example of a rigid magnetic recording disk with a servopattern formed by contact magnetic transfer (CMT) is shown in the planview FIG. 1A and the sectional view FIG. 1B. The magnetic recording disk10 comprises a rigid substrate 11, a thin film metal alloy (e.g.,CoPtCrB) magnetic recording layer 13 on the substrate and an outer layer15 (e.g., a protective amorphous carbon overcoat, which typically has alubricant, such as perfluoropolyether (PFPE), on its surface). The disk10 has an annular data portion or band 12 which is defined by an insidediameter (ID) 14 and an outside diameter (OD) 16. The sectional view ofFIG. 1B is taken along the track or circumferential direction and showssubstrate 11, recording layer 13 with typical magnetized portions 48,34, 38 making up part of the servo pattern, and outer layer 15. Duringoperation of the disk drive, the head reads or writes data on a selectedone of a number of concentric data tracks located between the ID 14 andOD 16 of the annular data band 12. To accurately read or write data froma selected track, the head is required to be maintained over thecenterline of the track. Accordingly, each time one of the servosectors, such as typical sector 18, passes beneath the head, the diskdrive's head positioning control system receives servo information fromthe servo blocks contained within the servo sector. The informationcontained in the servo blocks generates a position error signal which isused by the head positioning control system to move the head towards thetrack centerline. Thus, during a complete rotation of the disk 10, thehead is continually maintained over the track centerline by servoinformation from the servo blocks in successive servo sectors.

An expanded top view of a typical servo sector 18 and portions of threedata tracks is shown in FIG. 2. The three data tracks 20, 22, 24 areshown in outline. All of the shaded portions of FIG. 2 representmagnetized regions of the recording layer 13 that have been patterned bya CMT process. The “N” and “S” indicate the poles for each magnetizedregion. The non-shaded portions on FIG. 2 represent the regions ofrecording layer 13 that retain their magnetization from a DCmagnetization process prior to the CMT process. A portion of the servosector 18 is a servo field 30 that includes spaced-apart servo blocks,such as typical servo blocks 32, 34 and 36, 38. Also included in servosector 18 is a field 40 of radial stripes 42, 44, 46, 48 that are usedto provide synchronization and gain control for the subsequently readservo signals from servo blocks 32, 34 and 36, 38. Additionalinformation, e.g., timing marks indicating the beginning of a servosector and/or a coded pattern for identifying the specific servo trackby track number, may also be included in servo sector 18. The servoblocks 32, 34 and 36, 38 in servo field 30 and the radial stripes 42-48in the synchronization/gain field 40 are DC magnetized in the track orcircumferential direction of the disk, as indicated by the designations“N” and S” in FIG. 2.

The CMT master template made according to the method of the presentinvention is shown as it would be used in the CMT apparatus of FIG. 3,which is the CMT apparatus also described in the previously-citedco-pending application. A chamber 200 has an upper opening 202 with anouter periphery 204. The opening 202 is covered by the CMT mastertemplate. The CMT master template comprises a flexible plastic film 106supported at its outer perimeter by a rigid substrate 100. The plasticfilm 106 has a pattern of magnetic islands 114 corresponding to thepattern to be transferred to the slave disk. The chamber opening 202 issealed by clamp 206 and O-ring 208. The interior of chamber 200 has aninlet 209 connected to pressure regulator 210 which is connected to apressurized nitrogen source. A rotation stage 220 is located insidechamber 200 and supports a platform 222 that rotates about an axis 224.A permanent magnet 230 and a counterweight 240 for magnet 230 aremounted off-axis on the platform 222. The stage 220 is also movable inthe vertical Z-direction parallel to the axis 224 so that magnet 230 canbe positioned at the desired distance from plastic film 106. Therecording disk 10 to be patterned (the slave disk) is mounted on agripper arm 250 that is movable in the X-Y-Z directions above theplastic film 106. The movement of the gripper arm 250 and stage 220 iscontrolled by a motion controller, typically a PC. The chamber 200 ispressurized to move the plastic film 106 with its pattern of magneticislands 114 into contact with the slave disk 10. As the stage 220rotates, the magnetic field from magnet 230 creates a magnetized patternin slave disk 10 that replicates the pattern of magnetic islands 114 onthe plastic film 106 of the CMT master template.

A first method for making the CMT master template will be described withFIGS. 4A-4K, which are sectional views not to scale so that the featuresof the template can be seen. In FIG. 4A a rigid support structure orsubstrate 100 has a plastic film 106 adhered to it. The substrate 100 ispreferably semiconductor-grade single-crystal silicon with a first ortop surface 101 that supports the plastic film 106 and a second orbottom surface 103. The silicon substrate can be any commerciallyavailable Si wafer, such as a 5 in. Si wafer 550 μm thick. The plasticfilm 106 is preferably polyimide having a thickness in the range ofapproximately 5 to 25 μm. It can be adhered directly to the siliconsurface 101 by applying a liquid polyimide, such as by spin-coating,followed by curing. Some of the liquid polyimide types used areHitachi-DuPont Microsystems 2610, 2611 and 5811. The plastic film 106can also be adhered to the silicon surface 101 in sheet form with asuitable adhesive. Commercially available plastic sheets can bepolyethylene terephthalate (PET), naphthalate (PEN) or polyimide, suchas Melinex 453, Melinex 725, Melinex 561, Mylar D1, and Kadanex 1000,all available from DuPont. Also shown in FIG. 4A is an optional barrierlayer 104. Barrier layer 104 is applied to the silicon surface 101before the plastic film 106 if the silicon substrate 100 is intended tobe later removed by a wet etching process that might attack the plasticfilm 106. If the plastic film 106 is polyimide, then the optionalbarrier layer 104 can be a material such as chromium (Cr) or gold (Au)that is sputter deposited or evaporated to a thickness in the range ofapproximately 10 to 30 nm on the silicon substrate surface 101.

In FIG. 4B an optional etch-protect layer 108 is deposited on top of theplastic film 106. Etch-protect layer 108 improves the surface smoothnessof the plastic film 106 that is not intended to be etched. The preferredmaterial for etch-protect layer 108 is germanium (Ge) sputter depositedor evaporated to a thickness in the range of approximately 10-20 nm.Other materials for etch-protect layer 108 are chromium (Cr), tantalum(Ta) and tungsten (W).

In FIG. 4C a pattern of resist 110 has been formed on the plastic film106 or on the etch-protect layer 108 if it is used. The resist may be anelectron-beam (e-beam) resist such as polymethylmethacrylate (PMMA) thatis applied by spin-coating and then cured. The e-beam resist film isthen exposed to the e-beam in an e-beam lithography tool in the patterndesired for the CMT master template. The resist is then developed andremoved, leaving the pattern of resist 110.

In FIG. 4D the plastic film 106 is etched through the pattern of resist110 to form recesses in the plastic film 106. If a Ge etch-protect layer108 is used then the Ge is etched by reactive-ion-etching (RIE) in aCHF₃ gas to remove the Ge layer. This is followed by RIE of the plasticfilm 106 in an oxygen/argon (O₂/Ar) atmosphere. The RIE continues untilapproximately 50 nm of the plastic film 106 has been removed. Becausethe O₂ also attacks the resist, the surface of the plastic film 106 inthe non-recessed regions beneath the resist 110 may become roughened bythe RIE if the etch-protect layer 108 was not present between thenon-recessed plastic film 106 regions and the resist 110. Thus theoptional etch-protect layer 108 improves the surface smoothness of theplastic film 106 in the non-recessed regions.

In FIG. 4E, the resist 110 and etch-protect layer 108 have been removed.The resist is removed by conventional solvents such as acetone orN-Methylpyrrolidone (NMP). If the etch-protect layer 108 is Ge it isremoved by application of hydrogen peroxide (H₂O₂), such as by dippinginto the H₂O₂ for approximately 10 to 15 seconds.

In FIG. 4F, a chemical-mechanical-polishing (CMP) stop layer 112 isdeposited over the entire plastic film 106. The CMP stop layer 112 is amaterial substantially resistant to the CMP process so that the CMPprocess that removes material above the CMP stop layer essentially endswhen the stop layer is reached. In this first embodiment of the method,the CMP stop layer 112 is deposited not only over the non-recessedregions of the plastic film 106, but also into the recesses in theplastic film 106. The preferred materials for CMP stop layer 112 arediamond-like carbon (DLC) formed by ion-beam-deposition (IBD) to athickness in the range of approximately 10 to 50 nm and tantalum (Ta)sputter deposited to a thickness in the range of approximately 20 to 100nm. Other known CMP stop layer materials include one or more nitrides ofTa (TaNx) and titanium (TiNx), as well as Cr and NiCr alloy.

In FIG. 4G, the magnetic material layer 114 is deposited over the CMPstop layer 112 to fill the recesses in the plastic film 106. Themagnetic material is any soft (relatively low coercivity) magneticmaterial, such as NiFe(30/70) or NiFe(55/45) or NiFe(80/20) orNiFeCo(35/12/53) or FeCo(62/38) or other alloys of Ni, Fe and/or Co. Themagnetic material layer 114 can be deposited by evaporation orelectroplating or other known processes, but the preferred process is byIBD. The magnetic material layer 114 is deposited to a thickness in therange of approximately 100 to 300 nm.

Next the CMP is performed until the CMP stop layer 112 in thenon-recessed regions of the plastic film 106 is reached. This removesthe magnetic material above the CMP stop layer 112 in the non-recessedregions and a portion of the magnetic material above the recessedregions, but leaves the magnetic material in the recesses of the plasticfilm 106. The CMP process can use any slurry known to remove themagnetic material. The preferred CMP slurry for a NiFe magnetic materialis a KOH or NH₄OH based slurry with colloidal silica particles with anaverage particle size of between approximately 20 and 200 nm, such as aKlebosol® slurry product manufactured by Clariant. As shown in FIG. 4H,after the CMP process, the surface above the plastic film 106 has beenplanarized and includes the magnetic islands 114 separated bynonmagnetic regions of the CMP stop layer 112.

A second embodiment of the method is shown in FIGS. 5B, 5C, 5D, 5G and5H for comparison with corresponding FIGS. 4B, 4C, 4D, 4G and 4H of thefirst embodiment of the process. The primary difference is that in thesecond embodiment the CMP stop layer 112 is deposited on the plasticfilm 106 before the Ge etch-protect layer 108, as shown in FIG. 5B. Theformation of the pattern of resist 110 (FIG. 5C) is the same as in FIG.4C. The RIE (FIG. 5D) is the same as in FIG. 4D, except that followingthe RIE there is no CMP stop layer located in the bottom of the recessesor the walls of the recesses. After removal of the resist 110 and the Geetch-protect layer 108 the magnetic material layer 114 is deposited intothe recesses and is now in direct contact with the plastic film 106(FIG. 5G), instead of in contact with the CMP stop layer 112 (FIG. 4G).After CMP the magnetic islands and CMP stop layer regions are planarizedwith only magnetic material being located in the recesses (FIG. 5H),unlike in FIG. 4H where CMP stop layer material is located in therecesses as well as in the side walls of the recesses. The absence ofCMP stop layer material in the recesses and side walls enables themagnetic islands to be more precisely dimensioned.

In both embodiments of the method, after planarization by CMP, a thinprotective film 118 is deposited, as shown in FIG. 4I. The protectivefilm 118 may be a sputter deposited carbon film approximately 2 to 5 nmthick. Other materials for protective film 118 include SiNx (siliconnitride). In addition to or in place of the protective film 118, aplasma-polymerized 4 nm thick perfluorocarbon (PFC) overcoat can beapplied. The protective film 118 and PFC overcoat improve the durabilityand reduce water contamination of the master template.

After deposition of the protective film 118 and/or PFC overcoat, theupper surface of the CMT master template is complete. The remaining stepis to remove the plastic film 106 from the surface 101 of the siliconsubstrate 100. If the plastic film 106 is a plastic sheet adhered to thesilicon by an adhesive it is removed by simply peeling it off. However,if a liquid was applied to the silicon and then cured to form theplastic film 106, such as the polyimide film, then the preferred methodto remove it is to wet etch the silicon from the back surface 103. Asshown in FIG. 4J, in this method the silicon substrate 100 is placed ina cylindrical fixture 130 that has a wall 132. The second or bottomsurface 103 of silicon substrate 100 and the wall 132 form a sealedcontainer for the wet etchant, with the seal provided by an O-ring 134.The wet etchant 140 is placed into the container 130 and removes thesilicon from the back surface 103. The wet etching continues until allof the silicon has been removed in the area exposed to the etchant. Onetype of wet etchant for silicon is a mixture of hydrofluoric acid (HF)and nitric acid (HNO₃). If the optional barrier layer 104 has beenformed between the first surface 101 and the plastic film 106 then thebarrier layer 104 is resistant to the wet etchant so that the etchingstops when the barrier layer 104 has been reached. If the etchant is thesolution of HF and HNO₃, the preferred barrier layer 104 is a Cr filmapproximately 200 to 500 nm thick.

After removal of the plastic film 106, the CMT master template is asshown in FIG. 4K, and comprises the flexible plastic film 106 attachedat its outer perimeter to a rigid annular support 100 with its topsurface being the planarized magnetic islands 114 and stop layer regions112 and its bottom surface being the barrier layer 104.

While the present invention has been particularly shown and describedwith reference to the preferred embodiments, it will be understood bythose skilled in the art that various changes in form and detail may bemade without departing from the spirit and scope of the invention.Accordingly, the disclosed invention is to be considered merely asillustrative and limited in scope only as specified in the appendedclaims.

1. A contact magnetic transfer template comprising: a flexible plasticfilm having first and second opposite surfaces, the first surfacecontaining islands of soft magnetic material and nonmagnetic regions,the upper surfaces of the islands and nonmagnetic regions forming acontinuous substantially planar surface; a rigid silicon support,wherein only the perimeter of the plastic film is attached to thesilicon support; and a barrier layer on the second surface of theplastic film and formed of a material resistant to a wet etchant capableof etching silicon, the perimeter of the barrier layer being between thesilicon support and the plastic film.
 2. The template of claim 1 whereinthe plastic film is a polyimide film.
 3. The template of claim 1 whereinthe barrier layer is a material selected from the group consisting of Crand Au.
 4. The template of claim 1 wherein the nonmagnetic regions areformed of a chemical-mechanical-polishing (CMP) stop material.
 5. Thetemplate of claim 4 wherein the CMP stop material is selected from thegroup consisting of diamond-like carbon (DLC), Ta, one or more nitridesof Ta, one or more nitrides of Ti, Cr and NiCr alloy.
 6. The template ofclaim 1 further comprising a protective film over the magnetic islandsand nonmagnetic regions.
 7. The template of claim 6 further comprising aperfluorocarbon coating over the protective film.
 8. A contact magnetictransfer template comprising: an annulus formed of silicon; acircularly-shaped flexible polyimide film with a thickness between about5 and 25 microns and having first and second surfaces with the outercircumference of its second surface attached to the silicon annulus, thepolyimide film having on is first surface a pattern of magnetic islandsand nonmagnetic regions, the magnetic islands being formed of softmagnetic material, the nonmagnetic regions being formed of a materialselected from the group consisting of diamond-like carbon (DLC), Ta, oneor more nitrides of Ta, one or more nitrides of Ti, Cr and a NiCr alloy,and the upper surfaces of the magnetic islands and nonmagnetic regionsforming a continuous substantially planar template surface; and abarrier layer on the second surface of the polyimide film with its outercircumference located between the second surface of the plastic film andthe silicon annulus, the barrier layer formed of a material resistant toa wet etchant capable of etching silicon.
 9. The template of claim 8wherein the barrier layer is a material selected from the groupconsisting of Cr and Au.
 10. The template of claim 8 further comprisinga protective film over the magnetic islands and nonmagnetic regions. 11.The template of claim 10 further comprising a perfluorocarbon coatingover the protective film.